Sequencing batch reactor for sewage treatment and sewage treatment system comprising same

ABSTRACT

Disclosed is a sequencing batch reactor (SBR) for sewage treatment. The SBR is applicable to an energy-producing sewage treatment system. The SBR includes a treatment tank and a hybrid bacterial strain screening tank. The treatment tank removes ammonium contained in supernatant liquid using anaerobic ammonium-oxidizing (anammox) bacteria. The hybrid bacterial strain screening tank screen anammox bacteria granules out by passing the supernatant liquid discharged from the treatment tank through the hybrid bacterial strain screening tank. The SBR generates biogas using the anammox bacteria and reduces the nitrogen content in the supernatant liquid. The SBR can separate the anammox bacteria granules with high separation efficiency, thereby shortening sewage treatment time and recycling activated sludge, resulting in a dramatic decrease in the amount of waste sludge.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2017-0049522, filed Apr. 18, 2017 and Korean Patent Application No.10-2017-0077929, filed Jun. 20, 2017, the entire contents of which areincorporated herein for all purposes by these references.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure generally relates to a sequencing batch reactor(SBR) for sewage treatment and to a sewage treatment system includingthe SBR. More particularly, the present disclosure relates to asequencing batch reactor (SBR) for sewage treatment, which is capable ofimproving energy production efficiency of a continuous influent feedsewage treatment process performed in an energy-producing sewagetreatment system by lowering the content of nitrogen in sewage, and to asewage treatment system including the SBR.

Description of the Related Art

Conventional sewage treatment plants typically use an activated sludgeprocess, a combined form of an activated sludge process and anadditional process, or a modified activated sludge process.Specifically, in many countries other than Korea, ananoxic/anaerobic/oxic (A²/O) process, a UCT process, a VIP process, andthe like are generally used. However, these processes are not applicableto the domestic sewage treatment plant in Korea in which a combinedsewer system is used. The A²/O process is a technology improved from aconventional anaerobic-oxic (AO) process and is a biological treatmentprocess to remove nitrogen and phosphorous. A sewage treatment systemusing an A²/O process includes an anaerobic tank, an anoxic tank, and anaerobic tank and involves an internal recycle (also referred to asnitrifier recycle) for removing nitrate-nitrogen and an activated sludgerecycle. In the anaerobic tank, phosphorous release occurs underanaerobic conditions, resulting in microbial luxury uptake in theaerobic tank. In the anoxic tank, a denitrification process, in whichnitrate contained in internal return water returned from the aerobictank is converted into nitrogen, is performed so that nitrogen andphosphorous can be removed.

It is possible to reduce nutritive salts contained in sewage through theremoval of nitrogen and phosphorous by using the A²/O process. However,the A²/O process is a technology developed with focus only on reductionin nutritive salts in sewage, and it is unsatisfactory in terms ofremoval of nitrogen and phosphorous. Therefore, the A²/O process has aproblem of being unable to remove bacteria and microorganisms which arecontained in sewage and harmful to human body.

Most sewage treatment plants are operated based on biological treatmentin which pollutants are decomposed by microorganisms. Biologicaltreatment methods have proven their performance for a long time and aremost effective and safest treatment methods. However, such methods havea problem of producing a great amount of waste sludge.

Most waste sludge is a mass of microorganisms and organic matter.Therefore, it easily decays so that its treatment is problematic. Sofar, disposal of the waste sludge has been mainly relied on marinedumping and only a portion of the waste sludge has been landfilled orincinerated. The amount of waste sludge generated was more than 10,000tons per day in 2012, meaning more than a total of 3.65 million tons ofsludge annually, and it will continue to increase in the future.

With respect to the treatment of waste sludge, since 2002, marinedumping had been banned and policies for promoting conversion of organicwaste to renewable energy, such as waste recycling, waste reduction, andenergy production from waste, have been implemented. Specifically, inthe treatment of sludge using an anaerobic digestion tank, apretreatment process is carried out to increase the treatmentefficiency. The pretreatment techniques include: biological treatmentmethods using high temperature aerobic microorganisms; physicaltreatment methods using ultrasonic wave, hydrodynamic cavitation,thermal hydrolysis, or ball milling; chemical treatment methods usingozone treatment and alkaline chemical treatment; a complex treatmentmethod in which combinations of those methods are used; and electricaltreatment methods using electrolysis. However, these methods are notcost effective or have low sludge reduction efficiency. Therefore, it isdifficult to commercially use any of these methods.

Korean Patent No. 10-135458 discloses a sludge solubilization method forincreasing the digestion efficiency of the anaerobic digestion tank,where the waste sludge generated in a wastewater treatment process istreated with an alkali catalyst and methanol to soften or destroy thecell membrane of biodegradable microorganisms existing in the sludge toimprove the anaerobic digestion efficiency of the digestion tank.

The foregoing is intended merely to aid in the understanding of thebackground of the present disclosure, and is not intended to mean thatthe present disclosure falls within the purview of the related art thatis already known to those skilled in the art.

SUMMARY OF THE DISCLOSURE

Accordingly, an object of the present disclosure is to provide a sewagetreatment sequencing batch reactor capable of reducing an installationsite area for facilities thereof by having a simple structure, ofreducing a treatment process time, and of recycling activated sludge.

Another object of the present disclosure is to provide a sewagetreatment system capable of minimizing an installation site area forfacilities thereof by using the sewage water treatment SBR having asimple structure of reducing generation of byproducts and a treatmentprocess time, and of obtaining renewable energy by producing biogas.

The above and other objects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings andclaims.

Embodiments of the present disclosure are presented to make complete thedisclosure of the present disclosure and help those who are ordinarilyskilled in the art best understand the disclosure. The presentdisclosure may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the concept of thedisclosure to those skilled in the art.

In the drawings, the thicknesses of lines or the sizes of elements orlayers may be exaggeratedly illustrated for clarity and convenience ofdescription, and like components are denoted by like reference numerals.Moreover, the term “and/or” includes any and all combinations of one ormore of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting the disclosure. Asused herein, the singular forms “a,” “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise”,“include”, “have”, etc. when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components, and/or combinations of them but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components, and/or combinations thereof.

According to one embodiment of the present disclosure, the presentdisclosure provides to a sequencing batch reactor (SBR) for sewagetreatment, applicable to an energy-producing sewage treatment system,the sequencing batch reactor including: a treatment tank in whichsupernatant liquid decanted from a digestion tank is retained; and abioreaction tank for separating the supernatant liquid into anaerobicammonium-oxidizing (anammox) bacteria granules and liquid containingactivated sludge, wherein the bioreaction tank reciprocates a membraneto remove foreign materials attached to the membrane.

The bioreaction tank may be installed in a treated water storage tankconnected to the treatment tank.

The treated water storage tank may be provided with an anammox bacteriatransportation pipe for transporting anammox bacteria granules screenedout by the bioreaction tank to the treatment tank.

The bioreaction tank may include: a membrane support frame; a membranemodule attached to the membrane support frame; a moving unit connectedto the membrane support frame and moving the membrane support frame in areciprocating manner; and a sludge floatation unit arranged at a lowerend of the membrane support frame and floating sludge deposited in thetreatment tank.

The membrane module may include a plurality of porous membranes.

The porous membranes may have pores having a size of 50 to 150 μm.

The activated sludge may include at least one species selected from thegroup consisting of ammonia oxidizing archaea (AOA), ammonia oxidizingbacteria (AOB), and nitrite oxidizing bacteria (NOB).

The bioreaction tank may include an air feeding unit for feeding air topromote adsorption of organic matter contained in sewage to activatedsludge.

The bioreaction tank may include a membrane bioreactor (MBR) forseparating activated sludge onto which organic matter is adsorbed.

The anammox bacteria may be planctomycetes.

The anammox bacteria may be planctomycetes granules.

The SBR may further include a biogas collector for collecting biogasgenerated by the digestion tank.

According to a first aspect of the present disclosure, there is provideda sequencing bioreactor (SBR) for sewage treatment, applicable to anenergy-producing sewage treatment system. The SBR includes a treatmenttank and a hybrid bacterial strain screening tank. The treatment tankremoves ammonium contained in supernatant liquid by using anammoxbacteria. The hybrid bacterial strain screening tank filters thesupernatant liquid discharged from the treatment tank by passing thesupernatant liquid through a hybrid bacterial strain screening zoneprovided therein, thereby screening ammonium-oxidizing bacteria granulesout.

The hybrid bacterial strain screening tank may include: a housing havinga hybrid bacterial strain screening zone therein having a truncatedcircular conical shape; a feeding unit installed to extend through thehousing and the hybrid bacterial strain screening zone, the feeding unitfeeding the supernatant liquid to the hybrid bacterial strain screeningzone; and a recovery unit for recovering the supernatant liquid havingpassed through the hybrid bacterial strain screening zone.

The hybrid bacterial strain screening zone may have a truncated circularconical shape having an upper diameter larger than a lower diameterthereof, so that the supernatant liquid introduced into the hybridbacterial strain screening zone forms a vortex in the bacterial strainscreening zone due to a difference between the upper diameter and thelower diameter, thereby swirling downward in the bacterial strainscreening zone.

The hybrid bacterial strain screening zone may include a vortex-formingportion and a membrane, and the vortex-forming portion and the membraneare disposed respectively at an upper portion and a lower portion of thetruncated circular conical shape.

The sequencing batch reactor may further include an anammox bacteriatransport pipe such that anammox bacteria granules contained in thesupernatant liquid introduced into the hybrid bacterial strain screeningzone are screened out by the membrane and the anammox bacteria granulesthat are screened out are transported to the treatment tank through theanaerobic ammonium-oxidizing bacteria transport pipe.

The membrane has pores having a pore size of 50 to 150 μm.

The activated sludge may contain one or more species selected from thegroup consisting of ammonia oxidizing archaea (AOA), ammonia oxidizingbacteria (AOB), and nitrite oxidizing bacteria (NOB).

The anaerobic ammonium-oxidizing bacteria may be planctomycetes.

The anaerobic ammonium-oxidizing bacteria may be planctomycetesgranules.

According to another aspect of the disclosure, there is provided asewage treatment system including: a primary settling tank in whichpollutants in sewage settle to produce raw sludge and primary treatedwater; a bioreaction tank in which organic substances contained in theprimary treated water discharged from the primary settling tank areadsorbed onto activated sludge to form a flock, the floc is removed, anda denitrification process is performed; a secondary settling tank inwhich waste sludge contained in biologically treated water dischargedfrom the bioreaction tank is settled; a dehydration tank in which theraw sludge recovered from the primary settling tank and the waste sludgerecovered from the secondary settling tank is dehydrated; a digestiontank in which the raw sludge and the waste sludge dehydrated in thedehydration tank undergoes a anaerobic digestion process, therebygenerating biogas; and the sequencing batch reactor according to thefirst aspect, the sequencing batch reactor removing nitrogen containedin supernatant liquid discharged from the digestion tank.

The sequencing batch reactor may include a hybrid bacterial strainscreening tank for removing ammonium by reacting the supernatant liquiddischarged from the digestion tank with anaerobic ammonium-oxidizingbacteria, and separating anaerobic ammonium-oxidizing bacteria granulescontained in the supernatant liquid and activate sludge from each other.

The hybrid bacterial strain screening tank may include: a housing havinga hybrid bacterial strain screening zone therein, having a truncatedcircular conical shape; a feeding unit installed to extend through thehousing and the hybrid bacterial strain screening zone and feedingsupernatant liquid to the hybrid bacterial strain screening zone; and arecovery unit for recovering the supernatant liquid having passedthrough the hybrid bacterial strain screening zone.

The hybrid bacterial strain screening tank may include a vortex-formingportion provided at an upper portion thereof and a membrane provided ata lower portion thereof.

The hybrid bacterial strain screening tank may further include asupernatant liquid feeding unit for transporting supernatant liquidcontaining activated sludge to the primary settling tank.

The activated sludge includes one or more species selected from thegroup consisting of ammonia oxidizing archaea (AOA), ammonia oxidizingbacteria (AOB), and nitrite oxidizing bacteria (NOB).

The bioreaction tank may be equipped with an air feeder for feeding airsuch that organic substances in sewage are adsorbed onto the activatedsludge.

The bioreaction tank may include a hybrid bacterial strain screeningtank for separating the activated sludge onto which the organicsubstances are adsorbed.

The anaerobic ammonium-oxidizing bacteria may be planctomycetes.

The anaerobic ammonium-oxidizing bacteria may be planctomycetesgranules.

The sewage treatment system may further include a biogas collector forcollecting biogas generated from the digestion tank.

According to the present disclosure, the sequencing batch reactor (SBR)for sewage treatment generates energy in the digestion tank and reducesthe content of nitrogen contained in supernatant liquid by reacting thesupernatant liquid with anaerobic ammonium-oxidizing bacteria.Subsequently, the SBR supplies the supernatant liquid from which thecontent of nitrogen is reduced to a sewage treatment system, therebymaintaining an overall concentration of nitrogen lower than apredetermined level in the sewage over the whole sewage treatment systemand improving energy production efficiency of the sewage treatmentsystem.

In addition, since the SBR reaction tank is equipped with the membranebioreactor (MBR) and/or the hybrid bacterial strain screening tank, theSBR according to the present disclosure performs solid-liquid separationwith high separation efficiency, thereby reducing the treatment time. Inaddition, by recycling separated activated sludge, it is possible todramatically reduce the amount of waste sludge. Therefore, it ispossible to minimize the footprint of the sewage treatment system andincrease sewage treatment efficiency per site area.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description when taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a schematic configuration of asequencing batch reactor (SBR) for sewage treatment, according to oneembodiment of the present disclosure;

FIG. 2 is a diagram illustrating a hybrid screening tank for screeningand isolating microorganisms; and

FIG. 3 is a diagram illustrating a schematic configuration of a sewagetreatment system according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinbelow, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Thepresent disclosure may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be through and complete, and will fully convey the concept of thedisclosure to those skilled in the art.

Hereinafter, a sequencing batch reactor (SBR) for sewage treatment andan energy-producing sewage treatment system according to embodiments ofthe disclosure will be described below in conjunction with theaccompanying drawings.

FIG. 1 is a diagram illustrating a schematic configuration of asequencing batch reactor (SBR) for sewage treatment, according to oneembodiment of the disclosure. The SBR includes a treatment tank 100 anda hybrid bacterial strain screening tank 200. The treatment tank 100 isa vessel in which supernatant liquid (effluent) produced by a digestiontank is temporarily retained. To lower the content of ammonium containedin the supernatant liquid, the supernatant liquid is reacted withanaerobic ammonium-oxidizing (abbreviated to anammox) bacteria.

After the completion of the reaction, anammox granules resulting fromthe reaction between the anammox bacteria and the supernatant liquid arepresent in the supernatant liquid along with activated sludge. Theanammox granules and the activated sludge are separated by using thesizes of sludge particles and then separately recycled. The hybridbacterial strain screening tank 200 is used for this process.

The hybrid bacterial strain screening tank 200 will be described in moredetail with reference to FIG. 2.

The hybrid bacterial strain screening tank 200 includes a housingprovided with a hybrid bacterial strain screening zone 210 comprising atruncated circular conical shape, a feeding unit extending through thehousing and the hybrid bacterial strain screening zone 210 and feedingthe supernatant liquid to the hybrid bacterial strain screening zone210, and a recovery unit for collecting the supernatant liquid flowingthrough the hybrid bacterial strain screening zone 210.

The hybrid bacterial strain screening zone 210 is disposed inside thehousing, and the feeding unit is configured to extend through thehousing and the hybrid bacterial strain screening zone to feed thesupernatant liquid to the hybrid bacterial strain screening zone 210.The feeding unit may be composed of a pipe extending through the housingto be connected to the hybrid bacterial strain screening zone 210.

The supernatant liquid 110 discharged from the treatment tank 100 isintroduced into the hybrid bacterial strain screening zone 210 at aconstant flow rate. For example, the supernatant liquid 110 flows downinto the hybrid bacterial strain screening tank 200 from above, thenpasses through the hybrid bacterial strain screening zone 210, andfinally flows out.

Preferably, the hybrid bacterial strain screening zone 210 is of atruncated circular conical shape. When the diameter of the upper end ofthe hybrid bacterial strain screening zone 210 of the truncated circularconical shape is larger than that of the lower end thereof, thesupernatant liquid 110 forms a vortex while passing through the hybridbacterial strain screening zone 210 of the truncated circular conicalshape, thereby swirling down in the hybrid bacterial strain screeningzone 210.

Preferably, the hybrid bacterial strain screening zone 210 may include avortex-forming portion and a membrane 220. The vortex-forming portionand the membrane 220 are respectively disposed at an upper portion and alower portion of the truncated circular conical form. The supernatantliquid 110 forms a vortex in the vortex-forming portion when passingthrough the hybrid bacterial strain screening zone 210, and the vortexis discharged from the hybrid bacterial strain screening zone 210through the membrane 220 provided at the bottom of the hybrid bacterialstrain screening zone 210.

The membrane 220 has pores having a size of 50 to 150 μm. Therefore, theanammox bacteria granules which are larger than the pore size cannotpass through the membrane 220 but to remain in the hybrid bacterialstrain screening zone 210, but the activated sludge particles which aresmaller than the pore size and the supernatant liquid 120 containing theactivated sludge particles can be discharged from the hybrid bacterialstrain screening zone 210 through the membrane 220 and then introducedinto the internal space of the housing.

The supernatant liquid 120 stays in the housing until it reaches apredetermined liquid level and then overflows into a primary settlingtank through the recovery unit of the housing when the supernatantliquid 120 increases to reach or to be higher than the predeterminedlevel.

The anammox bacteria granules retained in the hybrid bacterial strainscreening zone 210 are collected and transported to the treatment tank100. The anammox bacteria granules transported to the treatment tank 100are returned to be reused in the treatment tank.

FIG. 3 is a diagram illustrating a schematic configuration of a sewagetreatment system according to one embodiment. The sewage treatmentsystem includes a primary settling tank 10, a bioreaction tank 20, asecondary settling tank 30, a dehydration tank 40, a digestion tank 50,and an SBR reaction tank 60.

According to the disclosure, sewage is first fed to the primary settlingtank 10, pollutants contained in the sewage settle down to the bottom ofthe primary settling tank 10 to become raw sludge which is laterrecycled, and supernatant liquid from which the pollutants (e.g., rawsludge) is removed is fed to the bioreaction tank 20. More specifically,when the sewage is fed to the primary settling tank 10, it separatesinto a layer of heavier substances (e.g., raw sludge) having a higherspecific gravity than water and into a layer of lighter substances(e.g., suspended solids) having a lower specific gravity than water.Through this process, about 40% of the total pollutants in sewage can beremoved.

Next, supernatant liquid resulting through the removal of raw sludgefrom the sewage in the primary settling tank 10 may be fed to thebioreaction tank 20.

The bioreaction tank 20 includes an aerobic tank, a hybrid bacterialstrain screening tank, and an anaerobic tank. More specifically, theaerobic tank allows organic substances contained in the supernatantliquid to be adsorbed onto activated sludge. The aerobic tank includesan inlet through which the supernatant liquid is fed to the aerobictank, a mixing cell for mixing the supernatant liquid and activatedsludge, and an aerobic reaction zone that is connected to the mixingcell and in which organic substances are adsorbed onto the activatedsludge. The activated sludge functions to adsorb organic substancescontained in sewage. Through this adsorption process, the pollutants canbe, at least partly or completely, removed in a short time.

The adsorption of organic substances to the activated sludge isperformed under aerobic conditions. To this end, an air feeder may beconnected to the aerobic reaction zone to feed air.

The aerobic reaction zone is provided to remove pollutants in sewage byusing activated sludge. Therefore, optimum operation conditions for theactivated sludge should be maintained.

That is, the aerobic reaction zone needs to maintain the followingoperation conditions: a temperature is maintained within a range ofvalues from 10 to 35° C., a retention time for which pollutants may besufficiently adsorbed onto activated sludge is secured, and a pH ofsewage is maintained within a range of values from 6.5 to 8.5.

According to the embodiment, sewage that is a target to be treated isfed to the aerobic reaction zone through the inlet, and the sewage ismixed with activated sludge so that organic substances can be adsorbedonto the activated sludge. The activated sludge includes at least one ofammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB), andnitrite oxidizing bacteria (NOB) so that organic substances can beadsorbed onto the activated sludge.

According to the embodiment, the mixing cell may be equipped with one ormore stirrers, thereby promoting mixing between the sewage and theactivated sludge.

In the present disclosure, although it is not necessary to limit theshape of the stirrer, it may be an impeller with multiple blades, forexample. Although it is not necessary to specifically limit the shape ofthe impeller-type stirrer, it is preferable that the impeller-typestirrer is structured such that an outer blade is bent toward a lowerend of an inner blade so that the blades can strongly push water suchthat a large amount of water can flow in a desired direction, therebymaximizing mixing efficiency.

When the stirrer has multiple blades, the multiple blades may have thesame size or different sizes. Preferably, the multiple blades may havedifferent sizes and may be arranged such that the size of each bladedecreases from the blade that is disposed at an upper portion of thereaction zone to the blade that is disposed at a lower portion of thereaction zone. In this case, a high mixing rate can be maintained whileinfluent (e.g., feed sewage) moves from the upper portion to the lowerportion of the reaction zone.

The value (e.g., G-value) of g force of the blade of the stirrer is notspecifically limited, and it may be determined depending on the scale ofmixing or flocculation or depending on the size of the reaction tank.However, for example, it may be preferably within a range of values from30 to 110 sec⁻¹.

According to the embodiment, a reaction aid (e.g., flocculant) may beadded to the sewage along with the activated sludge. The reaction aidmay be at least one selected from the group consisting of clay, calciumhydroxide, cationic flocculant, anionic flocculant, and non-ionicflocculant.

When the organic substances are adsorbed onto the activated sludge togrow to become a floc, the treated water resulting from the processperformed in the aerobic tank is supplied to the hybrid bacterial strainscreening tank connected to the aerobic tank. The activated sludge ontowhich the organic substances are adsorbed cannot pass through themembrane installed in the hybrid bacterial strain screening tank,thereby remaining as solid sludge in the tank. That is, the hybridbacterial strain screening tank separates the sewage into solids (e.g.,sludge) and liquid (e.g., primarily treated water).

According to the present disclosure, first organic substances containedin sewage are adsorbed onto activated sludge and flocculate in theaerobic tank of the bioreaction tank, and subsequently the sewage isseparated into solid (e.g., sludge) and liquid (e.g., primary treatedwater) by the hybrid bacterial strain screening tank. The primarilytreated water is then transported to the anaerobic tank to undergodenitrification. A description of the denitrification process performedin the anaerobic tank will not be set forth herein.

According to the present disclosure, it is possible to separatesolid-phase sludge having a small water content of only 70 to 80% fromsewage by using the hybrid bacterial strain screening tank of thebioreaction tank 20. In addition, unlike conventional membranebioreactors, the water treatment system of the present disclosure doesnot require an additional air feeder for removing foreign substancesattached to the membrane.

Since the hybrid bacterial strain screening tank is constructed andoperated in the same way as described above, a more specific descriptionthereof will be omitted here. That is, the hybrid bacterial strainscreening tank may be used in combination with the treatment tank of theSBR, or it also may be used in combination with the bioreaction tank 20.

Both of the treatment tank 10 and the bioreaction tank 20 of the SBRgenerate granular sludge by using anammox bacteria. At this time, thegenerated granular sludge is too large to pass through the membrane ofthe hybrid bacterial strain screening zone. Thus, the granular sludgefiltered out by the membrane of the hybrid bacterial strain screeningtank of the bioreaction tank 20 is collected and returned to a precedingstage so as to be reused. Meanwhile, the treated water passing throughthe membrane proceeds to the next treatment stage. That is, the anammoxbacterial granules 130 which were not able to pass through the hybridbacterial strain screening zone of the bioreaction tank 20 are returnedto the treatment tank 100 and reused there, and the supernatant liquid120 containing activated sludge, which passes through the hybridbacterial strain screening zone, is returned to the primary settlingtank 10 to be reused.

In the wastewater treatment system, pollutants contained in sewagesettle to become sludge in the primary settling tank 10, and theremainder of the sewage, which is treated water (e.g., liquid), istransported to the bioreaction tank 20. The treated water transported tothe bioreaction tank 20 undergoes an organic substance removal processand a denitrification process by sequentially passing through theaerobic tank, the hybrid bacterial strain screening tank, and theanaerobic tank of the bioreaction tank.

Secondary treated water that results from the denitrification processperformed in the anaerobic tank is retained in the secondary settlingtank 30 so that excess activated sludge (e.g., waste sludge) is removedfrom the secondary treated water, and then the resulting treated wateris disinfected and finally discharged to the outside of the watertreatment system.

The raw sludge and the excess activated sludge generated through thesettling process respectively in the primary settling tank and thesecondary settling tank are transported to the dehydration tank 40, andthen dehydrated. Next, thickened sludge resulting from the dehydrationprocess is transported to the digestion tank 50.

In the present disclosure, the digestion tank 50 performs an anaerobicdigestion process on the raw sludge and the excess activated sludge byusing anaerobic microorganisms.

The “anaerobic digestion” also may be referred to as “methanefermentation” that is a process in which organic substances contained inthe excess sludge are decomposed mainly into methane and carbon byvarious anaerobic microorganisms. Specifically, this process includes:liquefaction and hydrolysis for decomposing insoluble organic compoundsinto soluble monomers and short chain fatty acids (e.g., volatileorganic acids) including acetic acid, propionic acid, and butyric acid;gasification for converting these intermediate products into acetic acidand hydrogen gas (H₂); and methanogenesis for producing methane by usingproducts of the previous stage.

In the present disclosure, the digestion tank 50 treats the thickenedsludge and recovers energy from biogas (e.g., methane). Accordingly, thewater treatment system according to the present disclosure may include abiogas collector (not illustrated) for collecting biogas generated bythe digestion tank 50, and may further include a biogas membrane forseparating the biogas into methane and carbon dioxide as necessary.

In the present disclosure, the anaerobic digestion process performed inthe digestion tank 50 produces digested sludge that cannot be recycledand supernatant liquid. The digested sludge may be discarded or disposedand the supernatant liquid may be supplied to the SBR reaction tank 60.

The SBR reaction tank 60 is a sequential batch reactor so that asequencing batch activated sludge process is performed in the SBRreaction tank 60. In conventional SBR processes, one batch reactorfunctions as both of a reaction tank and a secondary settling tank sothat reaction of a sewage-and-sludge mixture, settling of pollutants,decanting of supernatant liquid, discharging of settled sludge, etc. arerepeatedly performed in the same tank.

In conventional sewage treatment systems, an anaerobic digestion processfor digesting thickened sludge is performed in the digestion tank 50,and the supernatant liquid resulting from the digestion process isreturned to the primary settling tank to be retreated. In that case, thesupernatant liquid decanted from the digestion tank 50 contains NH⁴⁺ orNO²⁻. Therefore, in the case of a continuous influent feed sewagetreatment process, the concentration of nitrogen continuously increaseswith time. Thus, a carbon-to-nitrogen (C/N) ratio in the bioreactiontank 20 comes to exceed 1, and eventually energy generation efficiencyof the digestion tank 50 is deteriorated.

In order to solve this problem, according to the present disclosure, thesupernatant liquid generated from the digestion tank 50 is transportedto the SBR reaction tank 60 to react with anammox bacteria, so that NH⁴⁺and NO²⁻ contained in the supernatant liquid is converted into N₂,resulting in removal of nitrogen.

According to the embodiment of the disclosure, planctomycetes are usedas the anammox bacteria. AOB bacteria generally used as activated sludgein the bioreaction tank 20 can convert about 50% of NH⁴⁺ into NO²⁻ intonitrogen (N₂). Meanwhile, planctomycetes used in the SBR reaction tank60 in the embodiment of the present disclosure can convert all of NH⁴⁺and NO²⁻ into N₂. Furthermore, planctomycetes generate granules having arelatively large size by being adsorbed on organic substances, incomparison with AOA, AOB, or NOB. Therefore, as described above, thegranules generated by the planctomycetes can be easily screened out bythe hybrid bacterial strain screening tank 200.

According to the present disclosure, it is possible to remove nitrogencontained in the supernatant liquid by transporting the supernatantliquid to the SBR reaction tank 60. Therefore, even in the case wheretreated water generated by the SBR reaction tank 60 is transported tothe primary settling tank 10, the C/N ratio equal to or lower than 1(e.g., C/N ratio≤1) can be maintained in the bioreaction tank 20, sothat energy production efficiency is not deteriorated even through acontinuous influent feed SBR process for sewage treatment.

The supernatant liquid transported to the SBR reaction tank 60 may beretained in the treatment tank 100. According to the present disclosure,the supernatant liquid transported to the treatment tank 100 undergoesan anaerobic digestion process by anaerobic ammonium-oxidizing bacteria,so that granules thereof are formed.

According to the present disclosure, the pore size of the membrane isset to be within a range of values from 50 to 150 μm so that thebacteria granules cannot pass through the membrane while bacteria suchas AOA, AOB, and NOB which are contained in the activated sludge canpass through the membrane in the bioreaction tank 20.

According to the present disclosure, the supernatant liquid and thebacteria, such as AOA, AOB, and NOB contained in the supernatant liquid,may be returned to the primary settling tank 10 via a treated water feedpipe.

Although the present disclosure has been described in conjunction withthe preferred embodiment and the accompanying drawings, the presentdisclosure should not be construed as being limited to the embodiment.Those skilled in the art will appreciate that various modifications,additions, and substitutions are possible, without departing from thescope and spirit of the disclosure as disclosed in the accompanyingclaims.

What is claimed is:
 1. A sequencing batch reactor (SBR) for sewagetreatment, the SBR comprising: a treatment tank as a reaction tankconfigured to discharge supernatant liquid in which ammonium containedin supernatant liquid is removed by using anaerobic ammonium-oxidizing(anammox) bacteria; and a hybrid bacterial strain screening tank as areaction tank configured to filter the supernatant liquid dischargedfrom the treatment tank by passing the supernatant liquid through ahybrid bacterial strain screening zone provided in the hybrid bacterialstrain screening tank, to screen out ammonium-oxidizing bacteriagranules, the hybrid bacterial strain screening tank comprising: ahousing comprising a hybrid bacterial strain screening zone of acircular frustum shape including an upper portion and a lower portion,the lower portion having an outer circumferential surface extending fromthe upper portion to a bottom of the lower portion, the hybrid bacterialstrain screening zone including a vortex-forming portion disposed at theupper portion, and a membrane disposed on the outer circumferentialsurface of the lower portion of the circular frustum shape andconfigured to discharge the supernatant liquid and particles ofactivated sludge from the hybrid bacterial strain screening zone throughthe membrane to be introduced into an internal space of the housing; afeeding unit installed perpendicularly with respect to a longitudinalaxis of the circular frustum shape so as to extend into the housing andcommunicate with the hybrid bacterial strain screening zone andconfigured to feed the supernatant liquid to the hybrid bacterial strainscreening zone; and a recovery unit for collecting and returning thesupernatant liquid passing through the hybrid bacterial strain screeningzone.
 2. The sequencing batch reactor according to claim 1, wherein thehybrid bacterial strain screening zone has a lower diameter and an upperdiameter larger than the lower diameter so that the supernatant liquidintroduced into the hybrid bacterial strain screening zone forms avortex in the bacterial strain screening zone due to a differencebetween the upper diameter and the lower diameter, thereby swirlingdownward in the bacterial strain screening zone.
 3. The sequencing batchreactor according to claim 1, further comprising an anaerobicammonium-oxidizing bacteria transport pipe such that anaerobicammonium-oxidizing bacteria granules contained in the supernatant liquidintroduced into the hybrid bacterial strain screening zone are screenedout by the membrane and the anaerobic ammonium-oxidizing bacteriagranules which are screened out are transported to the treatment tankthrough the anaerobic ammonium-oxidizing bacteria transport pipe.
 4. Thesequencing batch reactor according to claim 1, wherein the membrane haspores having a pore size between 50 and 150 μm.
 5. The sequencing batchreactor according to claim 1, wherein the activated sludge contains oneor more species selected from the group consisting of ammonia oxidizingarchaea (AOA), ammonia oxidizing bacteria (AOB), and nitrite oxidizingbacteria (NOB).
 6. The sequencing batch reactor according to claim 1,wherein the anaerobic ammonium-oxidizing bacteria are planctomycetes. 7.The sequencing batch reactor according to claim 1, wherein the anaerobicammonium-oxidizing bacteria are planctomycetes granules.
 8. A sewagetreatment system comprising: a primary settling tank in which pollutantsin sewage settle to produce raw sludge and primary treated water; abioreaction tank in which organic substances contained in the primarytreated water discharged from the primary settling tank are adsorbedonto activated sludge to form a flock, the floc is removed, and adenitrification process is performed; a secondary settling tank in whichwaste sludge contained in biologically treated water discharged from thebioreaction tank is settled; a dehydration tank in which the raw sludgerecovered from the primary settling tank and the waste sludge recoveredfrom the secondary settling tank is dehydrated; a digestion tank inwhich the raw sludge and the waste sludge dehydrated in the dehydrationtank undergoes a anaerobic digestion process, thereby generating biogas;and a sequencing batch reactor for removing nitrogen contained insupernatant liquid discharged from the digestion tank.
 9. The sewagetreatment system according to claim 8, wherein the sequencing batchreactor comprises a hybrid bacterial strain screening tank for removingammonium by reacting the supernatant liquid discharged from thedigestion tank with anaerobic ammonium-oxidizing bacteria, andseparating anaerobic ammonium-oxidizing bacteria granules contained inthe supernatant liquid and activate sludge from each other.
 10. Thesewage treatment system according to 9, wherein the hybrid bacterialstrain screening tank comprises: a housing to have a hybrid bacterialstrain screening zone of a truncated circular conical shape; a feedingunit installed to extend through the housing and the hybrid bacterialstrain screening zone and to feed supernatant liquid to the hybridbacterial strain screening zone; and a recovery unit to collect andreturn the supernatant liquid flowing through the hybrid bacterialstrain screening zone.
 11. The sewage treatment system according toclaim 10, the hybrid bacterial strain screening zone includes avortex-forming portion and a membrane, and the vortex-forming portionand the membrane are disposed respectively at an upper portion and alower portion of the truncated circular conical shape.
 12. The sewagetreatment system according to claim 10, wherein the hybrid bacterialstrain screening tank further comprises a supernatant liquid feedingunit for transporting supernatant liquid containing activated sludge tothe primary settling tank.
 13. The sewage treatment system according toclaim 8, wherein the activated sludge includes one or more speciesselected from the group consisting of ammonia oxidizing archaea (AOA),ammonia oxidizing bacteria (AOB), and nitrite oxidizing bacteria (NOB).14. The sewage treatment system according to claim 8, wherein thebioreaction tank is equipped with an air feeder for feeding air suchthat organic substances in sewage are adsorbed onto the activatedsludge.
 15. The sewage treatment system according to claim 8, whereinthe bioreaction tank includes a hybrid bacterial strain screening tankfor separating the activated sludge onto which the organic substancesare adsorbed.
 16. The sewage treatment system according to claim 8,wherein the anaerobic ammonium-oxidizing bacteria are Planctomycetes.17. The sewage treatment system according to claim 8, wherein theanaerobic ammonium-oxidizing bacteria are planctomycetes granules. 18.The sewage treatment system according to claim 8, further comprising abiogas collector for collecting biogas generated from the digestiontank.